1. Field of the Invention
The present invention relates to a solid phase reagent obtained by binding .beta.2-glycoprotein I (.beta.2-GPI) to a specific carrier, an assay method for antibodies specific to antiphospholipid syndrome using the solid phase reagent, a method for detecting antibodies specific to antiphospholipid syndrome and antibodies specific to infectious diseases differentially from each other, and a kit for use in the method.
2. Description of Related Art
Various assay methods including RIA and ELISA for anticardiolipin antibodies which are antibodies of the antiphospholipid family had been reported by Harris et al. (Lancet, iii: 1211, 1983), by Koike et al. (Clin. Exp. Immunol., 56: 193, 1984), etc.
However, those methods described above are not necessarily satisfactory since they involve problems in that the anticardiolipin antibodies cannot be assayed quantitatively or they involve problems in that the antibodies associated with infectious diseases cannot be assayed differentially from antibodies found in patients with antiphospholipid syndrome.
Recently, Matsuura et al. found that anticardiolipin antibodies associated with antiphospholipid syndrome do not recognize an immobilized cardiolipin (CL) but the complex of cardiolipin and .mu.2-glycoprotein I (alternatively termed apolipoprotein H or anticardiolipin cofactor). Further, they developed an assay method for antiphospholipid antibody determination based on the new findings described above, which can overcome the prior art problems as described above (Lancet, 336: 177, 1990, RINSHO MEN-EKI (Clinical Immunology), 22 (Suppl. 15): 170, 1990, WO 91/06006, J. Immunol., 148:3855, 1992).
The studies by Matsuura et al. revealed that anticardiolipin antibodies associated with antiphospholipid syndrome recognize the complex of cardiolipin and .beta.2-glycoprotein I. However, clinical significance of the antibodies has been still unclear. Under these circumstances, clarifying the clinical significance of anticardiolipin antibody binding should elucidate the pathogenesis of antiphospholipid syndrome. This is an important issue to be focused on in the future.
To solve the above-mentioned problems, it is important to develop a more convenient assay method having a high specificity and quantitative property. However, according to the conventional RIA and ELISA methods, it was impossible to detect differentially the antibodies directed to the complex of cardiolipin and .beta.2-glycoprotein I which is found in the patient with antiphospholipid syndrome from those directed to cardiolipin associated with infectious diseases such as syphilis, as described above. Although, the assay method improved by Matsuura et al. could provide differential detection of those antibodies, the preparation of solid phase reagents was still complicated on the other hand. It has thus been desired to establish a more convenient assay method.
Accordingly, an object of the present invention is to provide an assay method in a simpler manner for antibodies specific to the complex of cardiolipin and .beta.2-glycoprotein I.